(1) Field of the Invention
The invention relates to a display device, and more particularly to a liquid crystal display device of active matrix type.
(2) Description of the Related Art
A liquid crystal display device is generally an active matrix liquid crystal display device, including pixel transistors made of thin film transistors (Thin-Film-Transistor; hereinafter referred to as TFT) with respect to respective pixels formed in a matrix shape, which keeps display charge with the TFT pixel transistors in an OPEN state or in an electrically release state at any other time than the writing time.
Especially in these days, IPS element, particularly FFS element is widely used. This FFS device is formed by forming a flattening layer of resin on an array substrate, further superimposing an ITO layer, an insulating nitride film layer, and an ITO layer thereon.
A mobile phone is advanced to a smartphone, getting started to have the same function as a personal computer, with a remarkable increase of the display capacity expected. The screen size, however, cannot be formed so large; therefore, an extremely high display density is required.
The display density is represented by the display unit of ppi (pixel per inch: the number of pixels per inch) and as of the year 2013, the display unit of about 400 ppi is commercialized.
In our investigation, display resolution up to about 600 ppi can be assuredly recognized and finer definition is required. Even when clear dot recognition is not possible, it is said that a user requiring high quality requires high definition. Specifically, a high quality type of 700 ppi and 1000 ppi, exceeding 500 ppi, is required.
With advance to higher definition, there arises a problem such as a phenomenon of light leakage having a different color tone from the adjacent pixel. When a screen of a single color is displayed, “color mixture” with another color light mixed occurs disadvantageously. When the color mixture is seen in a front view, it is naturally improper, and when the color mixture is seen in left and right and oblique direction of a panel, it is also improper. It is an important point whether or not high yield and high accuracy can be achieved in the process of mass production.
In the conventional liquid crystal display device with a color filter formed on an opposite substrate, the primary cause of the color mixture is alignment deviation of an opposite substrate and an array substrate. In Japanese Patent No. 3738530, a technique of forming a color filter on the array substrate is disclosed in order to eliminate the effect of the alignment deviation of the array substrate and the opposite substrate with respect to the color mixture. The Japanese Patent No. 3738530 discloses a structure of forming a color filter on the array substrate in an island shape and easily forming a through-hole for conduction between electrodes on the array substrate.